1. Technical Field
The present invention relates to an image forming apparatus of the tandem type which has plural image forming stations. The stations are disposed along a travel direction (sub scanning direction) in which a transfer medium which may be a transfer belt or the like moves. Toner images formed by the respective image forming stations are superimposed one atop the other, and a color image is consequently formed.
2. Related Art
As JP-A-11-24356 specified below for instance discloses, among known image forming apparatuses such as copier machines, printers and facsimile machines is an image forming apparatus of the so-called tandem type. The apparatus has plural image forming stations which form toner images of mutually different colors from each other. The stations are disposed along a transfer belt which runs in a predetermined direction. In each image forming station, a latent image carrier such as a photosensitive drum for the associated toner color is disposed, and so is a laser beam scanner unit (image writer) for the photosensitive drum. Each laser beam scanner unit comprises a semiconductor laser element, a deflector and an imaging optical system such as an fθ lens. The semiconductor laser element emits dot light modulated in accordance with image data. The deflector deflects the light from the semiconductor laser element to a main scanning direction. The imaging optical system focuses the laser light deflected by the deflector as an image on the surface of the photosensitive member. The laser beam scanner units form latent images on the associated photosensitive drums and developer units make toner adhere to the photosensitive drums, whereby toner images corresponding to the latent images are formed. In this fashion, the toner images in the respective colors are formed and superimposed one atop the other on the surface of the transfer belt so that a color image is formed. The color image formed on the belt surface is transferred onto a transfer medium such as a paper sheet.
The apparatus described above comprises two drive motors which drive the respective sections of the apparatus such as a drive roller which drives the transfer belt, the photosensitive drums, etc. The photosensitive drums on which images in colors are to be formed are equipped with gears which are attached to central axes of the photosensitive drums, and the gears are linked to a first motor by a timing belt via an idle gear. Meanwhile, the photosensitive drum on which a black image is to be formed is equipped with a gear which is attached to a central axis of the photosensitive drum, and this gear is linked to a second motor via an idle gear. Further, a gear is attached to a central axis of the drive roller for the transfer belt, and linked also to the second motor via an idle gear. A gear is attached to a central axis of fixing apparatus as well, and linked also to the second motor via an idle gear.